1. Field of the Invention
The present invention relates to a method for the recovery of a tungsten-containing catalyst from coke containing other metallic components.
2. Description of the Prior Art
It is known to conduct coking processes in the presence of catalysts, including such catalysts as tungsten oxide on an alumina-containing support, see, for example, U.S. Pat. No. 4,269,696. During the coking reaction, catalyst present in the coking zone becomes associated with the coke product. The heavy hydrocarbonaceous oils used as feed for the coking process generally contain metallic contaminants, such as nickel, vanadium and iron. The coke which is produced from such metal-containing feeds contains at least a portion of the metallic contaminants that were present in the feed. When the coking process is conducted in the presence of a catalyst, it is desirable to recover the catalyst and to recycle it to the process. However, in recycling the catalyst, it is undesirable to recycle other metallic contaminants, e.g., vanadium and nickel, and thereby increase the concentration of the metallic contaminants in the coking zone. Several methods of recovering vanadium and/or nickel contaminants from coke are known.
U.S. Pat. No. 3,226,316 discloses a method of removing metal contaminants from coke using a gas-containing free oxygen and a halogen-containing material at a temperature of at least about 600.degree. F.
U.S. Pat. No. 3,214,346 discloses a method of removing ash constituents, such as vanadium, from fluid coke by oxidizing the coke with air at a relatively low temperature, cooling the particles and extracting them with an agent such an an alkali metal hydroxide and aqueous hydrogen chloride solution to remove the ash constituents from the coke particles.
U.S. Pat. No. 4,203,759 discloses a process for the preparation of a vanadium-containing metallic ash concentrate by heating a partially steam gasified coke comprising metallic components at a temperature below 1050.degree. F. in the presence of an oxygen-containing gas to burn the coke and produce a vanadium-containing metallic ash concentrate and alteration of the catalyst support.
Although there are methods available to remove the metal contaminants from the coke, a method was needed which would remove vanadium and nickel, but would minimize the removal of the metallic components of the catalyst and alteration of the catalyst support.
It has now been found that a tungsten-containing catalyst associated with coke containing nickel and vanadium may be recovered by a relatively low temperature burning to remove the coke followed by selective extraction of the nickel and vanadium.